Cilantro's El Perro

In "Roy Rogers McFreely", Roger first starts singing "El Perro" after Stan swallows all the horseradish. Later in the episode, the song is played during the car chase between Roger, Stan, Greg and Terry. Then, at the end, Roger dances under the motion sensor light, while Stan is watching him.

The song is originally performed by Cilantro (who is actually personified by Dan Navarro), but it seems that it has been made up just for the show.